Low‐concentration vemurafenib induces the proliferation and invasion of human HaCaT keratinocytes through mitogen‐activated protein kinase pathway activation

Cutaneous squamous cell carcinomas and keratoacanthomas commonly occur in patients treated with BRAF inhibitors. We investigated the effect of the BRAF inhibitor vemurafenib on normal immortalized human HaCaT keratinocytes to explore the mechanism of hyperproliferative cutaneous neoplasia associated with the use of BRAF inhibitors. Vemurafenib induced an increase in viable cell number in BRAF wild‐type cell lines (SK‐MEL‐2 and HaCaT) but not in BRAF mutant cell lines (SK‐MEL‐24 and G361). In HaCaT keratinocytes, a low concentration (2 μmol/L) of vemurafenib increased cell proliferation and activated mitogen‐activated protein kinase kinase/extracellular signal‐regulated kinase in a CRAF‐dependent manner. Invasiveness of HaCaT cells in a Matrigel assay significantly increased upon cultivation of cells with 2 μmol/L vemurafenib for 24 h. Gelatin zymography, reverse transcription polymerase chain reaction and western blot results revealed that 2 μmol/L vemurafenib treatment increased matrix metalloproteinase (MMP)‐2 and MMP‐9 expressions and activities in HaCaT cells. These results offer additional insight into the complex mechanism of paradoxical mitogen‐activated protein kinase signaling involved in hyperproliferative cutaneous neoplasias that arise after BRAF inhibition and suggest a possible role for MMP in tumor progression and invasion.